1. Field of the Invention
The present invention relates an exhaust gas treating system using polymer separation membrane, and more specifically to an exhaust gas treating system having an exhaust gas treating apparatus for carbon dioxide capture process which additionally removes harmful substances remaining in the gas discharged from the existing flue-gas desulfurization process by using separation membrane so as to efficiently carry out the carbon dioxide capture process.
2. Background Art
With an accelerated development of the technology of carbon dioxide capture and storage (hereinafter to be called ‘CCS’) for reducing the emission of carbon dioxide. Which is a representative greenhouse gas causing global warming, the level of carbon dioxide capture technologies has become high enough for commercialization. However, the development of the technology of treating harmful substances in the exhaust gas to be supplied to carbon dioxide capture process, which is indispensable for maintaining the performance of the carbon dioxide capture process and ensuring the durability of the process, is still unsatisfactory.
Coal, which has come to the fore as fossil fuel that has to be used more than any other fuels on a long-term basis, emits a lot of carbon dioxide due to its high carbon/hydrogen ratio and contains a relatively large quantity of harmful components such as sulfur. Since a high concentration of harmful components is emitted during combustion, it is essential to treat the harmful gases at the prestage of the carbon dioxide capture process.
FIG. 1 is a block diagram showing the exhaust gas treating system of a conventional coal burning thermal power plant including the carbon dioxide capture process.
With reference to FIG. 1, in the conventional exhaust gas treating system of a coal burning thermal power generation plant, contaminants are removed from the exhaust gas discharged from boiler 110 through flue-gas denitrification equipment 120, dust-collecting equipment 130 and flue-gas desulfurization equipment 140, before carbon dioxide is captured through carbon dioxide capture equipment 150 to be compressed and stored, and the exhaust gas is discharged into the atmosphere through a chimney 160.
As shown in FIG. 1, in the case of the conventional exhaust gas treating system of a coal burning thermal power plant, most of them are equipped with flue-gas desulfurization equipment 140 and flue-gas denitrification equipment 120, so about 90% of sulfur oxide (SOx) and nitrogen oxide (NOx) contained in the exhaust gas is removed before it is discharged.
However, even after the exhaust gas has passed through the desulfurization equipment 140 and denitrification equipment 120, the exhaust gas contains about 50 ppm to 100 ppm of SOx and NOx. If the exhaust gas containing sulfur oxide (SOx) and nitrogen oxide (NOx) which contain about 5% of nitrogen dioxide (NO2) is introduced into a carbon dioxide (CO2) capture process, the operation efficiency and economic effectiveness decrease due to degradation by an absorbent, especially an amine based absorbent or an alkali absorbent, used in the carbon dioxide (CO2) capture process.
In the conventional coal-burning thermal power plant, usually a selective catalyst reduction (SCR) process is used for the flue-gas denitrification process to treat nitrogen oxides (NOx). At this time, the removal efficiency is determined to comply with the emission standard, and the filling amount of catalyst or the feed of ammonia or urea solution is determined accordingly. At this time, in order to prevent the inflow of nitrogen dioxide (NO2) existing at about 5% in nitrogen oxides, additional apparatuses are necessary.
Coal contains heavy metal components (HAPs) such as mercury, and they are discharged into the atmosphere as vaporized form after combustion process. Thus, various methods such as a catalytic oxidation treatment apparatus, a halogenation treatment apparatus, or an activated carbon absorption tower has been developed to remove them.
in order to apply a CO2 capture process to a coal burning thermal power plant wherein exhaust gases containing various contaminants are discharged, a pretreatment process is required to maintain sulfur dioxide (SO2) below 10 ppm and to remove contaminants. Accordingly, there has been an increasing necessity that the existing flue gas desulfurization process is extensively modified or secondary flue-gas desulfurization equipment is additionally installed.
However, to maintain the concentration of discharged sulfur dioxide (SO2) below 10 ppm by raising the desulfurization efficiency to about 99.5% using the existing flue gas desulfurization process, the physical size of the absorption tower should be increased by a great deal and the packings and interior structure should be completely remodeled.
Also, to increase the circulation rate of the absorbent, basic equipment or apparatus such as a circulating pump should be added or replaced with the one having a large capacity. Therefore, in the case that CO2 capture equipment is to be added to the equipment that was already installed and is in operation, it is impossible to use the existing flue-gas desulfurization equipment by remodeling it and additional secondary flue-gas desulfurization equipment should be introduced.
FIG. 2 is a view showing a comprehensive pollutant exhaust gas treating system with secondary flue-gas desulfurization equipment (250) added to a conventional coal burning thermal power plant. The secondary flue-gas desulfurization equipment (250) is connected to the rear end of the first flue-gas desulfurization equipment (240) identical to the related art.
As shown in FIG. 2, in a conventional exhaust gas treating system 200 of a coal burning power plant, after removing contaminants from the exhausts gas discharged from a boiler 210 through flue-gas denitrification equipment 220, dust-collecting equipment 230 and the first flue-gas desulfurization equipment 240 and the secondary flue-gas desulfurization equipment 250, carbon dioxide is captured through carbon dioxide capture equipment 260, and it is compressed and stored, and the exhaust as is discharged into the atmosphere through a chimney 270.
On the other hand, the secondary flue-gas desulfurization equipment 250 is equipped with a mercury halogenation apparatus 251, a secondary desulfurization and mercury absorption apparatus 252, an ion absorption apparatus 253 and denitrification and absorption equipment 254, and these are connected in series. The denitrification and absorption equipment 254 is connected to the carbon dioxide capture equipment 260.
Since the secondary desulfurization equipment has various parts arranged in series to remove contaminants contained in the gas discharged from the first desulfurization equipment, a wide installation space and high installation cost are necessary. Also, an enormous installation cost is required and the operation cost for the processes also rapidly increases, so there is a problem of overall cost increase.